The invention set forth in this specification pertains to new and improved electrically controlled valves. The valves of this invention are presently intended for use with pneumatic fluids. It is considered, however, that these valves can either directly be employed with hydraulic fluids or can be easily modified so as to be suitable for use with hydraulic fluids in various different applications.
A wide variety of different electrically controlled valves are, of course, known. They are used in many different environments for many different purposes. Fortunately an understanding of the present invention does not require an understanding of the vast majority of such prior structures. It is considered, however, that an understanding of this invention is best predicated upon an understanding of two different types of prior electrically controlled valves.
Valves of the first of these types are constructed so as to utilize a torque motor in order to control the position of am armature so as to in turn either directly or indirectly control the flow from a source of fluid under pressure to a load so as to accomplish useful work. In general, these prior valves employing a torque motor are constructed so that the torque motor is in effect a separate and distinct element from the actual valve structure with which it is used. In effect, the torque motor in a valve of this type is coupled to the valve structure through the armature.
Such an armature is normally a comparatively rigid structure which is movably mounted on the valve structure at the location or locations where it passes more or less from the torque motor into the interior of the valve structure by an appropriate flexible or deformable member such as a bellows-like diaphragm or a comparative thin walled deflection tube. This type of deformable member is used to isolate the torque motor for the interior of the valve structure. Within the valve structure in this type of valve the armature can be utilized in different ways. It is conventional to use the armature so that an end of it is disposed between two opposed nozzles in such a manner that the position of the armature relative to the nozzles determines the amount of flow from the nozzles.
It is also known to form the armature in this type of valve so it has ends or bifurcations extending into two different separate chambers which are connected to one another by what may be referred to as load passages. Each of the load passages used in this type of structure is connected to an opening or nozzle in each of the separate chambers. With this type of structure when the armature is moved so as to control the flow between it and the two nozzles in one of the chambers it is concurrently moved so as to control the flow in the other of the chambers. The so-called "load" on a valve of this type is connected generally between or across the two load passages as, for example, by connecting one end of a cylinder serving as a load to one of the passages and the other end of such a cylinder to the other of the passages.
While this particular type of torque motor actuated valve employing such a bifurcated armature is considered to be effective and utilitarian it is also considered to be comparatively undesirable because of the close tolerances necessary to make a desirable valve of this type because of the relative slowness of the response time of the valve to an electric signal resulting from the inherent characteristics of the torque motor--armature type structure involved. This latter particularly involves the inertia of the armature used. Further, this type of valve is comparatively undesirable from an economic standpoint because of the costs involved in manufacturing a valve of this type. In this connection it is noted that while a torque motor is not prohibitively expensive to manufacture that such a motor is still a separate element which, on a comparative basis, is somewhat undesirably expensive to construct.
Valves of the second type which are important to an understanding of this invention are those valves which are constructed so as to utilize a piezoelectric strip as an actuator so as to control flow from opposed orifices. Known valves of this type utilize a piezoelectric strip cantilevered so that it's unsupported end is located in a chamber between two opposed orifices corresponding to the opposed nozzles commonly utilized in connection with the armature on the torque motor.
With structures of this type the relative position of the strip with respect to the two different orifices can be used so as to control flow from both of these nozzles so as to in turn change the pressures in passages connected to different parts of a load used to perform different useful work. Valves of this type are different from those torque motor valves described in the preceding discussion in which the bifurcations or spaced ends of an armature extend into two different chambers in several ways. They employ only a single chamber. The position of the piezoelectric strip in such a valve alone is responsible for any variable pressure change in this type of valve. In addition, of course, there are other obvious differences.
Piezoelectric valves as described in the preceding are considered to be disadvantageous for different reasons than the torque motor operated valves previously discussed. It is considered that these known piezoelectric valves can not provide an adequate pressure differential between the two different orifices to perform many different types of tasks normally associated with different types of loads such as cylinders as indicated in the preceding discussion. This is considered to be extremely significant.
Further, these prior valves have apparently been constructed so as to utilize relatively small orifices. This is considered rather surprising since other related valves utilizing piezoelectric strips have been constructed so that such a strip is used in controlling the flow from a single comparatively large opening or port to the interior of a chamber from which the emitted fluid passes through one or more openings or ports which are spaced significantly from the piezoelectric strip. In any event, the utilization of such small orifices obtaining a significant pressure drop is disadvantageous in that such an orifice can only pass or convey a limited amount of fluid and inasmuch as such an orifice can become clogged rather easily.
This particular matter of an orifice or nozzle becoming clogged is of comparative importance in connection with any pneumatic or hydraulic servo valve. When an orifice or similar opening in any such a valve becomes clogged with one or more contaminant particles there is a significant danger of the valve either not performing in an intended manner and/or one or more parts of the valve breaking. This can be particularly significant in valves such as the torque motor type valves indicated in the preceding discussion where, the spacing between nozzles and an end of an armature is comparatively restricted in nature even at the comparatively extreme position of the armature. This is because of the possibility of a particle becoming lodged generally between the nozzle and the armature. This is a different type of blocking or clogging action than is caused by a particle merely plugging up a comparatively restricted orifice. Clogging of this type has the potential of interfering with the operation of the torque motor used.
As a result of this clogging problem it has normally been considered necessary to utilize both of the types of valves indicated in the preceding discussion with comparatively expensive filters capable of removing comparatively small particles of contaminants and concurrently causing a significant pressure drop between the ends of the filter. The latter is, of course, undesirable in these instances where it is desirable to maintain as much of a pressure differential as possible across a load so as to accomplish a significant amount of useful work.